The desire to reduce Green House Gas emissions and lower dependency on fossil fuels enhanced the introduction of intermittent renewable energy sources such as Wind, solar PV, hydroelectric and others into the grid. While this trend has positive effects towards those tasks, it is also accompanied by new type of grid problems such as instability, fluctuations and mismatch between demand and production of electricity. Forecasts made up to 2020 and on show that the massive introduction of renewables results in a significant quantity of surplus renewable energy during day time where total supply may exceed total demand. The over-capacity that may last for hours during the daytime is a burden that must be solved. Cutting off any power producing facility and forcing it to work at reduced capacity reduce the plant efficiency and potential income. Since large electricity storage is unavailable at this time the other option is to create new immediate users to utilize the surplus energy. Such users are: electric vehicle charging, pumped hydro and ice making for midday cooling. However, all those are limited in capacity. In face of the inefficiency of forced load following, every effort that can be made to switch off or store large amount of production potential such as heat or pressure head without causing technical or economic damage is welcomed.
In spite of their low thermodynamic potential, low grade heat sources like geothermal and industrial waste-heat-recovery, which drive steam and Rankine Cycle Power Plants, are being more widely used these days not only because they do not require fossil fuel, but also because, contrary to solar and wind, they provide base-load and not intermittent power.
The geothermal and recovered waste heat plants share the grid load-following and mainly the demand for dispatching problem with all grid connected power plants.
As these heat sources flow continuously and preferably should not be disturbed, the dispatching is very inefficient when the heat which is not used is lost.
In case grid control demands to reduce production, the heat supply to the Rankine cycle must be reduced to adjust the output to the demand but the brine production pump or steam well valves cannot always work in varying flow rate for fear of damage to the well and in such cases, in order to minimize well suction problems the production well continues to pump the regular rate of hot fluid supply.
This is done by having the heat carrying fluid bypass the Rankine Cycle (FIG. 1b) and later it is injected into the injection wells together with the heat depleted fluid exiting from the Rankin cycle that worked on partial load.
Because the wasted heat has to be disposed of, and in case of geothermal, production and injection pumps are, in site specific cases, not stopped without damaging the wells, the dispatching is inefficient because the lost heat is not recoverable.
Consequently, the present invention provides a power plant that overcomes the shortcomings of prior art power plants particularly those of geothermal power plant.
Other advantages of the invention will become apparent as the description proceeds.